Digital Electronics: Principles, Devices and Applications

Flip-Flops and Related Devices 367+V CC555R 1t ONt OFFt7 8 4 3v oR 22,65 1C0.01(a)v oov C—V23 CC—V13 CC(b)tFigure 10.10 (a) Astable multivibrator using timer IC 555, (b) astable multivibrator relevant waveforms and(c, d) modified versions of the astable multivibrator using timer IC 555.10.2.2.2 Monostable Multivibrator Using Timer IC 555Figure 10.11(a) shows the basic monostable multivibrator circuit configured around timer 555. A triggerpulse is applied to terminal 2 of the IC, which should initially be kept at +V CC . A HIGH at terminal2 forces the output to the LOW state. A HIGH-to-LOW trigger pulse at terminal 2 holds the output inthe HIGH state and simultaneously allows the capacitor to charge from +V CC through R. Rememberthat a LOW level of the trigger pulse needs to go at least below +V CC /3. When the capacitor voltageexceeds +2V CC /3, the output goes back to the LOW state. We will need to apply another trigger pulse to